Bio 1150 1st Edition Lecture 24Current LectureTopic Discussed: Resource Acquisition & Transport in Vascular PlantsWater/mineral in the xylem move by bulk flow driven by transpiration- Water is pulled up to top of the plant- There is some pushing of water by root pressure due to pumping of minerals into xylem, but pressure is smallo Guttation-pushing water sap out of plantCohesion-tension hypothesis explains how transpiration pulls water up- Transpiration- causes the “pull” with negative water potential (pressure), then cohesion transmits the pull along the entire planto Mesophyll cells- water evaporation causes negative water potential pressure- Cohesion- attractive force between each water molecule- Adhesion - attractive force between the water molecule and the xylem wall- Transpirational pull goes from the stomata, through the xylem, through the roots, all the way into the soil solutionSoil water potential= -.3, its not 0 because of solutes in the water- Spongy mesophyll- a lot of air space- Sun causes the water potential gradient- Tension= -pressureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Loss of cohesion and subsequent air bubbles cause cavitation (embolism)- Xylem embolisms- bubbles- block flowStomata balance the need for CO2 for photosynthesis with water loss through transpiration- 95% of water loss is through stomata- Stomata expands with lots of water- Less water= less carbon dioxide= less photosynthesis- Stomatal density is controlled by genetics and by environment- Desert plants - less stomata than forest plants- Stomatal density has decreased due to increases in CO2Control of stomatal opening and closing- Turgid guard cells open stoma (kidney shaped)- Triggered by opening of K+ channelsTriggers to stomatal opening/closing- In the morning (stomata open)o Blue-light receptorso CO2 depletiono Internal circadian clock- biological rhythm ( 24 hrs)- Environmental stresses (stomata close)o Wind- because it speeds up evaporationo High temperature- also speeds up evaporationo Abscisic Acid (a hormone) produced in response to water deficiency, seen in drought plantsAdaptations in xerophytes- Oleander- stoma in crypt- pocket of leaves, not epidermal, water vapor gets trapped in pocketo Slows evaporation- Spines- reflect light, regulates temperature- Ocotillo- doesn’t make leaves when its too dry- Phenology- relation between phenomenon and timeTranslocation- movement of photosynthetic products through the phloemPhloem sap moves sugars from source to sink- Phloem sap -contains amino acids, hormones and minerals- Sink- stores sugar- Sugar is loaded into phloem usually through active transport- Sucrose-main sugar moves (very little sugar in xylem)- Sugar loaded into phloem by active transport- Through plasmodesmata or membrane in phloem- Proton pump in symplastPhloem movement is bulk flow by positive pressure (developed my Munch)- Loads sugar from the leaf- Uptake of water- Unloads sugar in the sink- Water goes to xylem to be recycled- Hydrostatic pressure- pressure build up from water, builds positive pressureSource sink relationships can be investigated with radiolabelling
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